Neuron, Vol. 37, 499--511, February 6, 2003, Copyright 2003 by Cell Press

s and Gerstein, der retina. These neurons tend to fire synchronously 1988; Frostig et al., 1990). We have now developed an far more frequently than expected by chance. We pres- efficient algorithm that can detect concerted activity of ent an efficient algorithm to identify what groups of arbitrarily large groups of neurons while circumventing cells cooperate in this way. Such groups can include the combinatorial explosion of the brute force approach. up to seven or more neurons and may account for Finally, one must be able to interpret what messages more than 50% of all the spikes recorded from the are conveyed by neural firing, to test whether concerted retina. These firing patterns represent specific mes- firing patterns play a special role. The opportunities for sages about the visual stimulus that differ significantly this are greatest at the sensory or motor periphery of from what one would derive by single-cell analysis. the nervous system, simply because the va